1. Field of the Invention
The present invention relates to a combined display panel in which a second display panel is combined with or overlapped on a first display panel. Such a combined display panel is used as a combination instrument panel for an automobile, a train or an airplane.
2. Description of Related Art
A combined display panel to be used as an automobile instrument panel in which an additional display panel such as an electroluminescent panel is combined with a conventional display panel has been proposed hitherto. The additional display panel serves to display various information which has been necessitated in recent years in addition to conventional information such as vehicle speed, engine speed, amount of fuel and coolant temperature. An instrument panel of an automobile, especially of a high grade automobile, is covered with a dimming filter having a low transparency for a design purpose. Such an instrument panel is sometimes referred to as a black-out meter. In this case, high luminance of display is required to show information clearly. Usually, the additional display panel such as an electroluminescent panel does not have a sufficiently high luminance for the black-out meter. It is possible to make an electroluminescent panel having such a high luminance, but it becomes expensive. In addition, a high power is consumed if such a high luminance panel is used.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide a combined display panel, in which a second display panel having luminance lower than that of a first display panel is used and yet a display of the second panel is clearly visible through a low transparency dimming filter.
A whole display surface of the combined display panel having a first panel and a second panel, luminance of which is lower than that of the first panel, is covered with a dimming filter having low transparency for an ornamental design purpose. Transparency of the dimming filter is made high in a wave-length region of the light emitted from the second panel, so that brightness imbalance between the first and second panels is alleviated or eliminated. Also, the transparency of the dimming filter is made high in another wave-length region of light, color of which is complementary to the color of the light emitted from the second panel, so that color shift in the display of the first panel is avoided. In this manner, the brightness imbalance and the color shift are avoided at the same time. Preferably, the level of the transparency of the dimming filter in the two wave-length regions in which it is enhanced is made higher than an average transparency level in a wave-length region covering a whole visible light. It is also preferable to make both transparency levels enhanced in two wave-length regions equal so that the color shift in the display of the first panel is further reduced to substantially zero.
A multi-color or a full color display panel may be used as the second panel which is combined with the first panel. In this case, the transparency of the dimming filter is made higher than the average transparency, in color regions covering the light emitted from the multi-color or full color display panel. Preferably, the transparency is made higher also in the color region complementary to the emitted light. Color filters may be used to constitute the multi-color or full color display panel.
To further enhance the advantage of the dimming filter having a high transparency in a specific wave-length region, it is most preferable to use a display panel, as the second panel, which emits light having a sharp peak in that specific wave-length region, such as an electroluminescent panel. Such an electroluminescent panel may be transparent or non-transparent. If the transparent panel is used, it may be overlapped on a part of the first panel, and if the non-transparent panel is used, it may be mounted on the first panel at a place where it does not interfere with the display of the first panel.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.